This invention relates generally to medical devices and methods for locating the coronary sinus of a heart and preferably placing an electrical lead for use with an implantable pulse generator.
Many cardiac disorders, such as bradycardia, tachycardia and ventricular fibrillation, for example, involve abnormalities of cardiac rhythm or rate. Implantable electrical pulse generators are commonly used to treat such disorders. Modern implantable pulse generators include an hermetically sealed housing containing control electronics and a battery, and have standard connectors to which implantable electrical leads can be connected. Such leads include insulated conductors and one or more exposed electrodes near the distal end of the lead for electrically connecting the pulse generator to one or more chambers of the heart. Sensing electrodes sense the electrical activity of the heart so that electrical markers of the electrocardiogram such as the P-wave or R-wave can be detected. Stimulating electrodes conduct pulses of electrical energy from the pulse generator to excitable cardiac tissue. Often both types of electrodes are employed, with the nature and timing of the stimulation pulses being related to the sensed electrical activity. Selected placement of the leads and electrodes permits delivery of therapeutic electrical pulses appropriate to the disorder to be treated.
Lead systems for use with modern implantable pulse generators can include single lead systems and multiple lead systems, with single or dual chamber sensing or therapy. Some systems provide four-chamber sensing and therapy. Examples of such systems can be found in Dual Chamber Cardiac Pacing from a Single Electrode, U.S. Pat. No. 5,265,601; Bi-atrial and/or Bi-ventricular Sequential Cardiac Pacing Systems, U.S. Pat. No. 5,902,324; Bi-ventricular Pacing Method, U.S. Pat. No. 6,223,079; and Multiple Channel Sequential Cardiac Pacing Method, U.S. Pat. No. 6,122,545, all incorporated by reference.
Although leads and electrodes can be applied directly to the epicardium via thoracotomy, it is generally preferred to insert the leads endovascularly into a chamber of the heart, when possible. In most single lead systems, the lead is passed through the superior vena cava, right atrium and tricuspid valve, and into the right ventricle. The electrode is fixed within the right ventricle usually at the apex position. In many multiple lead systems and some single lead systems, one lead is passed through the superior vena cava, right atrium and coronary sinus, generally with the aid of fluoroscopy, and fixed within the great vein or a deep coronary vein to locate the electrode in proximity to the left atrium or left ventricle.
Determining the location of the coronary sinus and placing a lead therein can be difficult. The lead must traverse an angle to enter the orifice of the coronary sinus in the wall of the right atrium. The difficulty of locating the coronary sinus and placing a lead therein is especially great in patients with congestive heart failure and dilated cardiomyopathy. In such patients, the heart is enlarged and the location of the coronary sinus can vary significantly from the location in a heart with normal anatomy. Nevertheless, the ongoing need to place endovascular cardiac leads in patients with an unusually disposed coronary sinus is expected to increase. This is because of the emerging use of implantable pulse generators to treat congestive heart failure.
Implantable pulse generators may be particularly useful for treating congestive heart failure (xe2x80x9cCHFxe2x80x9d) manifested by conduction defects or other cardiomyopathies. In a healthy person, the electrical conduction system of the heart sends signals to the chambers of the heart that cause them to contract in a precise pattern to pump blood throughout the circulatory system. In people with congestive heart failure, however, the electrical conduction system is often impaired and fails to coordinate the contractions of the heart""s chambers. In many patients with CHF, the left and right ventricles no longer contract in the usual synchronized manner. This can reduce cardiac output, leading to symptoms such as shortness of breath, fatigue, and swelling of the feet and ankles.
A promising therapy for treating congestive heart failure through the use of implantable pulse generators is bi-ventricular pacing, also known as cardiac re-synchronization. By sensing and pacing the left and right ventricles separately, the desired timing of the contractions of the ventricles can be obtained. This will result in an increase in cardiac output.
Bi-ventricular pacing involves placement of right and left ventricular pacing leads. The procedure for placing a pacing lead within a right ventricle is well known and has been effectively practiced for decades. In contrast, it is not desirable to place a pacing lead within the left ventricle. A lead passing through the left atrium and mitral valve into the left ventricle could interfere with complete closure of the valve, thereby impairing the performance of the left ventricle in pumping oxygenated blood throughout the body. Also, pacing leads may be a site of clot formation. Such clots, if dislodged, may cause serious problems in-the arterial circulation system, e.g., stroke. Pacing of the left ventricle can be achieved by placing a lead into a branch of the coronary sinus that overlies the left ventricle. As noted above, placing a left ventricular pacing lead into the coronary sinus can be extremely difficult even when performed by the most experienced electrophysiologists.
Preformed catheters have been used to permit access to the coronary sinus via the superior vena cava and right atrium. The use of such preformed catheters is complicated in patients with CHF and dilated cardiomyopathy because the location of the coronary sinus is quite variable. In recent clinical trials of bi-ventricular pacing, cannulation of the coronary sinus was attempted by experienced and expert electrophysiologists who cannulate the coronary sinus daily for arrhythmia testing. Despite their experience and expertise, the coronary sinus was successfully accessed only 85 percent of the time.
If bi-ventricular pacing is to become a widely used treatment for congestive heart failure, then reliable and easy access to the coronary sinus must be provided. There are insufficient numbers of experienced electrophysiologists to accommodate the demand for this therapy. The present invention permits cardiologists and others without daily experience accessing the coronary sinus to do so reliably. Other medical procedures that require endovascular access to the coronary sinus likewise will be facilitated by the present invention. An example of such a procedure is electrophysiologic testing when the coronary sinus is difficult to locate or cannulate.
The present invention relates to the medical procedure of accessing the orifice of the coronary sinus for the purpose of placing a medical device adjacent to or through the orifice. One such medical device is a permanent left ventricular pacing lead. Other medical devices include temporary sensing or pacing catheters for electrophysiologic testing.
According to one aspect, the present invention involves locating the orifice of the coronary sinus by sensing characteristics of blood emerging from the coronary sinus into the right atrium. One characteristic that is especially correlated with blood from the coronary sinus is oxygen content. The percent oxygen saturation in the coronary sinus is among the lowest in the human body. Other characteristics correlated with blood from the coronary sinus are lower pH and higher CO2 concentration. By sensing the oxygen concentration, pH, CO2 or other characteristic at the distal end of a medical device placed within the right atrium, and by steering the distal end of the medical device toward a region of lower oxygen concentration, lower pH or higher CO2 concentration, for example, the location of the orifice of the coronary sinus can be determined. Once the orifice of the coronary sinus is located, the medical device can be introduced into the coronary sinus or used to establish a pathway for guiding another device into the coronary sinus. One such medical device is a left ventricular pacing lead.
The present invention also permits determination of oxygen saturations in other vascular structures. This may be particularly important in patients with congenital heart disease as well as in patients in whom specific organ venous and arterial oxygen saturations are needed to guide medical therapy.
According to another aspect of the invention, a steerable oximetric catheter includes an elongate cannula having a proximal end and a distal end. A blood oxygen sensor is connected to the cannula and is disposed to sense percent oxygen saturation of blood at the distal end of the cannula. The blood oxygen sensor generates a signal indicative of percent oxygen saturation. An oximetry display is responsive to the signal and is capable of displaying sensed percent oxygen saturation in a form understandable by an operator. A steering mechanism is operably connected to the cannula and selectively operable by an operator to deflect the distal end of the cannula toward a region of relatively low percent oxygen saturation.
Once the coronary sinus is located, a pacing lead can be inserted through the cannula to be fixed proximate to the coronary sinus or inserted into and fixed into the great vein or a coronary vein extending from the coronary sinus. The steerable catheter then can be removed. Alternatively, once the coronary sinus is located, a hollow sheath can be advanced over the steerable catheter and held at the coronary sinus. The steerable catheter then can be removed and the pacing lead can be inserted through the hollow sheath to have its distal end fixed in the coronary sinus or a coronary vein extending from it. The hollow sheath then can be removed.
The present invention also includes a kit comprising a steerable oximetric catheter and a sheath used to locate the pacing lead.
Further aspects and advantages of the present invention are apparent from the following description of preferred embodiments and methods, made with reference to the drawings.